In the chaos that is family life, it seems the only thing that's constant is change. The biggest and most dramatic changes usually have to do with losing and switching jobs. This will directly influence your income, which has a big impact on your budget. Ideally, having already been on a budget, you will have saved up for an emergency fund to use in the event of losing a job. But you'll want to make your budget stretch even more during that time, just in case.
Whenever your long-term goals change, revisit your budget to re-evaluate your situation. Perhaps you'll find that a new baby is on the way, or a family member is diagnosed with a medical condition that will require expensive treatments. Or, as time goes on, your priorities could simply change. You may decide that you'd rather delay that European vacation, and instead put your savings toward a down payment on a bigger house. Each major change in your situation or priorities will require looking at your budget in a new light and making adjustments.